ADT7476 Analog Devices, Inc., ADT7476 Datasheet - Page 45

• Manufacturer Part Number: ADT7476
• Description: Dbcool Remote Thermal Controller And Voltage Monitor
• Manufacturer: Analog Devices, Inc.

Programming the PWM
The PWM
mum PWM duty cycle for each output to be configured
anywhere from 0% to 100%. This allows the minimum PWM
duty cycle to be set in steps of 0.39%.
The value to be programmed into the PWM
given by
Example 1: For a minimum PWM duty cycle of 50%
Example 2: For a minimum PWM duty cycle of 33%
PWM
Register 0x64, PWM1 Minimum Duty Cycle = 0x80 (50% default)
Register 0x65, PWM2 Minimum Duty Cycle = 0x80 (50% default)
Register 0x66, PWM3 Minimum Duty Cycle = 0x80 (50% default)
Note on Fan Speed and PWM Duty Cycle
The PWM duty cycle does not directly correlate to fan speed in
RPM. Running a fan at 33% PWM duty cycle does not equate to
running the fan at 33% speed. Driving a fan at 33% PWM duty
cycle actually runs the fan at closer to 50% of its full speed. This
is because fan speed in %RPM generally relates to the square
root of the PWM duty cycle. Given a PWM square wave as the
drive signal, fan speed in RPM approximates to
STEP 5: PWM
PWM
system runs under the automatic fan speed control loop. For
maximum system acoustic benefit, PWM
possible but should be capable of maintaining the processor
temperature limit at an acceptable level. If the THERM temper-
ature limit is exceeded, the fans are still boosted to 100% for
fail-safe cooling.
There is a PWM
of this register is 0xFF and has no effect unless it is programmed.
Value (decimal) = 50/0.39 = 128 (decimal)
Value = 128 (decimal) or 80 (hex)
Value (decimal) = 33/0.39 = 85 (decimal)
Value = 85 (decimal) or 54 (hex)
% fanspeed =
Value (decimal) = PWM
MIN
MAX
Registers
is the maximum duty cycle at which each fan in the
MIN
registers are 8-bit registers that allow the mini-
MAX
MAX
PWM
limit for each fan channel. The default value
FOR PWM (FAN) OUTPUTS
MIN
Duty
MIN
Registers
/0.39
Cycle
×
10
MAX
MIN
should be as low as
register is
Rev. B | Page 45 of 72
Programming the PWM
The PWM
maximum PWM duty cycle for each output to be configured
anywhere from 0% to 100%. This allows the maximum PWM
duty cycle to be set in steps of 0.39%.
The value to be programmed into the PWM
given by
Example 1: For a maximum PWM duty cycle of 50%
Example 2: For a minimum PWM duty cycle of 75%
PWM
Register 0x38, PWM1 Maximum Duty Cycle = 0xFF
(100% default)
Register 0x39, PWM2 Maximum Duty Cycle = 0xFF
(100% default)
Register 0x3A, PWM3 Maximum Duty Cycle = 0xFF
(100% default)
Value (decimal) = PWM
Value (decimal) − 50/0.39 = 128 (decimal)
Value = 128 (decimal) or 80 (hex)
Value (decimal) = 75/0.39 = 85 (decimal)
Value = 192 (decimal) or C0 (hex)
MAX
PWM
Figure 56. PWM
PWM
Registers
100%
MAX
MAX
MIN
0%
registers are 8-bit registers that allow the
Below the THERM Temperature Limit
MAX
T
MIN
Determines Maximum PWM Duty Cycle
MAX
MAX
Registers
/0.39
TEMPERATURE
MAX
register is
ADT7476